1. Field of the Invention
The present invention relates to an antenna structure, and more particularly to an antenna structure used in a communication device.
2. The Related Art
Antennas are widely used in various communication devices, such as mobile phones and notebook computers. Taking the mobile phones as an example, with the wireless communication technology, outboard antennas have been superseded gradually by built-in antennas. Furthermore, accompanying with the trend of miniaturization for the communication devices, the mobile phones are designed to be more and more light and portable for consumers to use, then the internal space of the mobile phones is limited. So the dimension of the built-in antennas should be correspondingly reduced to be small enough for being assembled in the limited space of mobile phones.
Among the present wireless technologies, wireless communication frequency bands for mobile phones include global system for mobile communications (GSM) band about 850 MHz, extended global system for mobile communications (EGSM) band about 900 MHz, digital cellular system (DCS) band about 1800 MHz and personal communication services (PCS) band about 1900 MHz. However, if the conventional antennas used in mobile phone support two or more frequency bands, it may increase dimension, which is undesirable in the circumstance where the sizes of the mobile phones are limited.